Printing liquids are used in many applications such as painting, gravure and press printing, xerographic printing using liquid toners, and ink-jet printing. Printing liquids typically comprise a colorant in a liquid media or vehicle. Examples include paints, liquid toners, and inks. The vehicle may be organic-based (solvent-based) or water-based (aqueous-based). The colorant may be dye or pigment. The printing liquid may further include additional ingredients based on the particular application.
Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, or textiles. Essentially, ink-jet printing involves the ejection of fine droplets of ink onto print media in response to electrical signals generated by a microprocessor.
There are two basic means currently available for achieving ink droplet ejection in ink-jet printing: thermally and piezoelectrically. In thermal ink-jet printing, the energy for drop ejection is generated by electrically-heated resistor elements, which heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble, resulting in the expulsion of ink through nozzles associated with the resistor elements. In piezoelectric ink-jet printing, the ink droplets are ejected due to the vibrations of piezoelectric crystals, again, in response to electrical signals generated by the microprocessor. The ejection of ink droplets in a particular order forms alphanumeric characters, area fills, and other patterns on the print medium.
Ink-jet printers offer low cost, high quality printing with relatively noise-free operation. As such, ink-jet printers have become a popular alternative to other types of printers.
In general, a successful ink set for color ink-jet printing should have the following properties: good crusting resistance, good stability, proper viscosity, proper surface tension, good color-to-color bleed alleviation, rapid dry time, no negative reaction with the vehicle, consumer-safety, good permanence (e.g., smearfastness, lightfastness, waterfastness), and low strike-through. When placed into a thermal ink-jet system, the ink set should also be kogation-resistant and have stable drop ejection performance (e.g. little or no drop velocity degradation over the time).
Regardless of whether an ink is dye-based or pigment-based, ink-jet inks commonly face the challenge of color-to-color or black-to-color bleed control. The term "bleed," as used herein, is defined to be the invasion of one color into another, once the ink is deposited on the print medium, as evidenced by a ragged border therebetween. Bleed occurs as colors mix both on the surface of the paper substrate as well as within the substrate itself. The occurrence of bleed is especially problematic between a black ink and an adjacently-printed color ink because it is all the more visible. Hence, to achieve good print quality, bleed should be substantially reduced or eliminated such that borders between colors are clean and free from the invasion of one color into the other. Several approaches have been utilized in controlling bleed between the printed images, many of which utilize reactive ink mechanisms.
Various solutions to the problem of black to color and color to color bleed have been proffered. Some solutions involve changing the ink environment to reduce bleed. For instance, heated platens and other heat sources, along with specially formulated paper, have been employed to reduce bleed. However, heated platens add cost to the printer, and specially formulated paper is more expensive than "plain" paper. Thus, using external paraphernalia to reduce bleed in ink-jet color printing is generally not cost effective. Another commonly employed method for reducing bleed involves the use of bleed control algorithms in ink-jet printers to provide borders between colors that are clean and free from the invasion of one color into another; however, such algorithms slow down the printer.
Other proposed solutions to the problem of bleed involve changing the composition of an ink-jet ink. For example, surfactants have been effectively used to reduce bleed in dye-based ink formulations; see, e.g., U.S. Pat. No. 5,106,416 entitled "Bleed Alleviation Using Zwitterionic Surfactants and Cationic Dyes," issued to John Moffatt et al., U.S. Pat. No. 5,116,409 entitled "Bleed Alleviation in Ink-Jet Inks", issued to John Moffatt, and U.S. Pat. No. 5,133,803 entitled "High Molecular Weight Colloids Which Control Bleed", issued to John Moffatt, all assigned to the same assignee as the present application. However, surfactants increase the penetration rate of the ink into the paper, which may also result in the reduction of edge acuity. Moreover, the addition of surfactant-containing inks could cause puddles on the nozzle plates of the printhead, leading to poor drop ejection characteristics. Other solutions specific to dye-based ink compositions, disclosed in patents assigned to the present assignee, are found in U.S. Pat. No. 5,198,023, entitled "Cationic Dyes with Added Multi-Valent Cations to Reduce Bleed in Thermal Ink-Jet Inks," issued to John Stoffel; U.S. Pat. No. 5,181,045, entitled "Bleed Alleviation Using pH Sensitive Dyes," issued to James Shields et al.; and U.S. Pat. No. 5,428,383, entitled "Method and apparatus for preventing color bleed in a multi-ink printing system," issued to Shields et. al.,"; all assigned to the same assignee as the present application.
Shields et. al., U.S. Pat. No. 5,428,383 discloses a method for printing multi-color images on a substrate in which color bleed between adjacent colored regions is controlled by providing a first ink composition comprising a first colorant; providing a second ink composition comprising a second colorant and a precipitating agent which will react with the first colorant in the first ink composition in order to form a precipitate therefrom; applying the first ink composition to the substrate in a first region thereon; applying the second ink composition to the substrate in a second region thereon, the second region being directly adjacent to and in contact with the first region; and reacting the precipitating agent in the second ink composition with the first colorant in the first ink composition at a position on the substrate where the first region contacts the second region so that the precipitate is formed at the position in order to prevent color bleed between the first ink composition in the first region and the second ink composition in the second region.
At times, formulating liquids with enhanced print quality performance, such as bleed performance, leads to degradation in printability and reliability performance.
Therefore, a need exists for an ink-jet liquid with enhanced bleed alleviation while maintaining good reliability and pen performance.